AndroidStudio学习笔记（五）小实战

实战

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1. 制作9-patch图片
   使用draw9patch.bat文件制作。打开后导入图片，可以在图片的四个边框绘制一个个的小黑点，在上边框和左边框绘制的部分表示当图片需 要拉伸时就拉伸黑点标记的区域，在下边框和右边框绘制的部分表示内容会被放置的区域。使 用鼠标在图片的边缘拖动就可以进行绘制了，按住Shift键拖动可以进行擦除。
2. 添加RecyclerView依赖库：
   implementation ‘com.android.support:recyclerview-v7:28.0.0’
3. 修改activity_main.xml中的代码:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#d8e0e8" >

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/msg_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <EditText android:id="@+id/input_text"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:maxLines="2" />
        <Button android:id="@+id/send"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="发送" />
    </LinearLayout>
</LinearLayout>

4. 新建Msg实体类:

public class Msg {
    public static final int TYPE_RECEIVED = 0;
    public static final int TYPE_SENT = 1;
    private String content;
    private int type;

    public Msg(String content, int type) {
        this.content = content;
        this.type = type;
    }
    public String getContent() {
        return content;
    }
    public int getType() {
        return type;
    }
}

5. 编写RecyclerView子项的布局，新建msg_item.xml，代码如下:

public class MsgAdapter extends RecyclerView.Adapter<MsgAdapter.ViewHolder>{
    private List<Msg> mMsgList;

    static class ViewHolder extends RecyclerView.ViewHolder {
        LinearLayout leftLayout;
        LinearLayout rightLayout;
        TextView leftMsg;
        TextView rightMsg;
        public ViewHolder(View view) {
            super(view);
            leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
            rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
            leftMsg = (TextView) view.findViewById(R.id.left_msg);
            rightMsg = (TextView) view.findViewById(R.id.right_msg);
        }
    }
    public MsgAdapter(List<Msg> msgList) {
        mMsgList = msgList;
    }

    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate (R.layout.msg_item, parent, false);
        return new ViewHolder(view);
    }

    public void onBindViewHolder(ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            // 如果是收到的消息，则显示左边的消息布局，将右边的消息布局隐藏
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        } else if(msg.getType() == Msg.TYPE_SENT) {
            // 如果是发出的消息，则显示右边的消息布局，将左边的消息布局隐藏
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

    public int getItemCount() {
        return mMsgList.size();
    }
}

6. 要创建RecyclerView的适配器类，新建类MsgAdapter ，代码如下:

public class MsgAdapter extends RecyclerView.Adapter<MsgAdapter.ViewHolder>{
    private List<Msg> mMsgList;

    static class ViewHolder extends RecyclerView.ViewHolder {
        LinearLayout leftLayout;
        LinearLayout rightLayout;
        TextView leftMsg;
        TextView rightMsg;
        public ViewHolder(View view) {
            super(view);
            leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
            rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
            leftMsg = (TextView) view.findViewById(R.id.left_msg);
            rightMsg = (TextView) view.findViewById(R.id.right_msg);
        }
    }
    public MsgAdapter(List<Msg> msgList) {
        mMsgList = msgList;
    }

    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate (R.layout.msg_item, parent, false);
        return new ViewHolder(view);
    }

    public void onBindViewHolder(ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            // 如果是收到的消息，则显示左边的消息布局，将右边的消息布局隐藏
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        } else if(msg.getType() == Msg.TYPE_SENT) {
            // 如果是发出的消息，则显示右边的消息布局，将左边的消息布局隐藏
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

    public int getItemCount() {
        return mMsgList.size();
    }
}

7. 最后修改MainActivity中的代码，来为RecyclerView初始化一些数据，并给发送按钮加入事件响 应，代码如下所示：

public class MainActivity extends AppCompatActivity {

    private List<Msg> msgList = new ArrayList<>();
    private EditText inputText;
    private Button send;
    private RecyclerView msgRecyclerView;
    private MsgAdapter adapter;
    private String MSG_Rec[]={
            "睡也是你，醒也是，无孔不入也是你。吃饭想你，走路想你，望穿秋水还是你~",
            "送你一朵花，做一枚发卡，别在你的心间~",
            "我多希望人生如梦，梦里都是诗，写的是我和你~",
            "我感动得再也不说出话^o^只能简单做一个复读机了....."};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        initMsgs(); // 初始化消息数据

        inputText = (EditText) findViewById(R.id.input_text);
        send = (Button) findViewById(R.id.send);
        msgRecyclerView = (RecyclerView) findViewById(R.id.msg_recycler_view);

        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        msgRecyclerView.setLayoutManager(layoutManager);
        adapter = new MsgAdapter(msgList);
        msgRecyclerView.setAdapter(adapter);

        send.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                int temp;
                String content = inputText.getText().toString();
                if (!"".equals(content)) {
                    Msg msg = new Msg(content, Msg.TYPE_SENT);
                    msgList.add(msg);

                    //回复消息2-4-6
                    temp = msgList.size()/2-1;
                    Msg msgRec;
                    if (temp<4){
                        msgRec = new Msg(MSG_Rec[temp], Msg.TYPE_RECEIVED);
                    }else {
                        msgRec = new Msg(content+"?", Msg.TYPE_RECEIVED);
                    }
                    msgList.add(msgRec);

                    adapter.notifyItemInserted(msgList.size() - 1);
                    // 当有新消息时， 刷新RecyclerView中的显示
                    msgRecyclerView.scrollToPosition(msgList.size() - 1);
                    // 将 RecyclerView定位到最后一行
                    inputText.setText(""); // 清空输入框中的内容
                }
            }
        });
    }

    private void initMsgs() {
        Msg msg1 = new Msg("hi~", Msg.TYPE_RECEIVED);
        msgList.add(msg1);
    }
}